/Engine/Source/Runtime/MeshDescription/Public/MeshDescription.h
Adds a new triangle to the mesh with the given ID. This will also make an encapsulating polygon, and any missing edges.
void CreateTriangleWithID ( const [FTriangleID](API\Runtime\MeshDescription\FTriangleID) TriangleID, const [FPolygonGroupID](API\Runtime\MeshDescription\FPolygonGroupID) PolygonGroupID, [TArrayView](API\Runtime\Core\Containers\TArrayView)< const [FVertexInstanceID](API\Runtime\MeshDescription\FVertexInstanceID) > VertexInstanceIDs, [TArray](API\Runtime\Core\Containers\TArray)< [FEdgeID](API\Runtime\MeshDescription\FEdgeID) > * OutEdgeIDs )